Researchers Examine Isolation's Effect on MRSA Transmission

Many studies have examined methicillin-resistant Staphylococcus aureus (MRSA) control measures, but few have been planned prospective single intervention studies in the endemic setting. Researchers from the Victorian Infectious Diseases Service of Royal Melbourne Hospital and the Department of Medicine at the University of Melbourne, both in Melbourne, Australia, investigated whether active surveillance and contact precautions (CP) reduced MRSA transmission. In a presentation at the International Conference on Prevention & Infection Control (ICPIC) held in Geneva, Switzerland June 29-July 2, 2011,
Marshall, et al. report on their study in which they collected and analyzed data to avoid confounding (of MRSA acquisition with length of stay) and serial dependence due to colonization pressure (CoPr) in accordance with ORION guidelines.

This was an interrupted time series in a tertiary ICU. Standard precautions only were used for control patients regardless of MRSA status. In the intervention period, rapid PCR was used to detect MRSA colonized patients, who were then cared for in CP. The researchers used a generalized estimating equation (GEE) with each patient-day being the unit of interest. The predictor variables were both time-dependent (antibiotic usage, hand hygiene and infection control precaution compliance and CoPr) and time-invariant covariates (co-morbidities, sex and age) and intra-individual risk correlation was adjusted for using the GEE framework.

The primary outcome measure was the effect of the intervention on MRSA acquisition, adjusting for CoPr and individual and ward covariates. The relative risk of MRSA acquisition was 0.40 (95%CI 0.24-0.65). Secondary measures include the effect of colonized patients in the ward (RR 4.38; 95% CI 1.00-19.21) and the phase-colonized patient interaction, with a reduced risk from colonized patients in the intervention phase to 0.41 (95% CI 0.14-1.18) compared with the control phase.

Marshall, et al. demonstrated a clinically significant effect of isolation on MRSA transmission. The researchers say their planned single intervention study is unique because of near-complete observations due to short intervals between swabs and full documentation of CoPr and time-varying risk factors.

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